1) Field of the Invention
The invention relates to compatibilized blends of polyamides in polyesters, a method for forming such compositions, and to containers made from such compositions. Specifically the compositions have less yellowness than previous blends. The blends can be used as passive gas barriers, or active oxygen scavengers with the addition of a transition metal catalyst.
2) Prior Art
Plastic materials have been replacing glass and metal packaging materials due to their lighter weight, decreased breakage compared to glass, and potentially lower cost. One major deficiency with polyesters is its relatively high gas permeability. This restricts the shelf life of carbonated soft drinks and oxygen sensitive materials such as beer and fruit juices.
Multilayer bottles containing a low gas permeable polymer as an inner layer, with polyesters as the other layers, have been commercialized. Blends of these low gas permeable polymers into polyester have not been successful due to haze formed by the domains in the two-phase system. The preferred polyamide is a partially aromatic polyamide containing meta-xylylene groups, especially poly(m-xylylene adipamide), MXD6.
The MXD6 bulletin (TR No. 0009-E) from Mitsubishi Gas Chemical Company, Inc., Tokyo Japan, clearly shows that the haze of a multilayer bottle containing a layer of 5 wt-% MXD6 is ˜1% compared to 15% for a blend of the same 5 wt-%.
However, the use of partially aromatic polyamides as the low gas permeable polymer gives an increase in the yellowness of the resultant container.
U.S. Pat. No. 4,501,781 to Kushida et al. discloses a hollow blow-molded biaxially oriented bottle shaped container comprising a mixture of polyethylene terephthalate (PET) resin and a xylylene group-containing polyamide resin. Both monolayer and multilayer containers are disclosed, but there is no information on the color of the bottles.
U.S. Pat. No. 5,650,469 to Long et al. discloses the use of a terephthalic acid based polyester blended with low levels (0.05 to 2.0 wt-%) of a polyamide to reduce the acetaldehyde level of the container. These blends produced lower yellowness containers than a corresponding blend made from a dimethyl terephthalate based polyester, but are still unsatisfactory for the higher levels required to significantly lower (decrease) the gas permeability.
U.S. Pat. Nos. 5,258,233, 5,266,413 and 5,340,884 to Mills et al. discloses a polyester composition comprising 0.05 to 2.0 wt-% of low molecular weight polyamide. At a 0.5 wt-% blend of MXD6 the haze of the bottle increased from 0.7 to 1.2%. No gas permeation or color data is given.
U.S. Pat. No. 4,837,115 to Igarashi et al. discloses a blend of amino terminated polyamides with PET to reduce acetaldehyde levels. There was no increase in haze with the addition of 0.5 wt-% MXD6, but at 2 wt-% the haze increased from 1.7 to 2.4%. No gas permeation or color data is given.
U.S. Pat. No. 6,239,233 to Bell et al. discloses a blend of acid terminated polyamides with PET that has reduced yellowness compared to amino terminated polyamides. No gas permeation data is given.
U.S. Pat. No. 6,346,307 to Al Ghatta et al. discloses the use of a dianhydride of a tetracarboxylic acid to reduce the dispersed domain size of a blend of MXD6 in PET. The examples did not give color data, but at a 10 wt-% MXD6 blend level the oxygen permeability was reduced from 0.53 to 0.12 ml/bottle/day/atm and the carbon dioxide permeability was reduced from 18.2 to 7.02 ml/bottle/day/atm.
U.S. Pat. No. 6,444,283 to Turner et al. discloses that low molecular weight MXD6 polyamides have lower haze than higher molecular weight MXD6 when blended with PET. The examples did not give color data, but at a 2 wt-% MXD6 (Mitsubishi Chemical Company grade 6007) the oxygen permeability of an oriented film was reduced from 8.1 to 5.7 cc-mil/100 in2-atm-day compared to 6.1 for the low molecular weight MXD6.
U.S. Pat. No. 4,957,980 to Koyayashi et al. discloses the use of maleic anhydride grafted copolyesters to compatibilize polyester-MXD6 blends.
U.S. Pat. No. 4,499,262 to Fagerburg et al. discloses sulfo-modified polyesters that give an improved rate of acetaldehyde generation and a lower critical planar stretch ratio. Blends with polyamides were not discussed.
Japanese Pat. No. 2663578 B2 to Katsumasa et al. discloses the use of 0.5 to 10 mole % 5-sulfoisophthalte copolymers as compatibilizer of polyester-MXD6 blends. No color data was given.
The use of a transition metal catalyst to promote oxygen scavenging in polyamide multilayer containers, and blends with PET, has been disclosed in the following patents, for example.
U.S. Pat. Nos. 5,021,515, 5,639,815 and 5,955,527 to Cochran et al. disclose the use of a cobalt salt as the preferred transition metal catalyst and MXD6 as the preferred polyamide. There is no data on the color or haze of the polyamide blends.
U.S. Pat. Nos. 5,281,360 and 5,866,649 to Hong, and U.S. Pat. No. 6,288,161 to Kim discloses blends of MXD6 with PET and a cobalt salt catalyst. There is no data on the color or haze of the polyamide blends.
U.S. Pat. No. 5,623,047 to You et al. discloses the use of a catalyst composition containing an alkali metal acetate, preferably 30 ppm cobalt acetate to mask the yellowness in polyesters polymerized from terephthalic acid.
US Pat. Application 2003/0134966 A1 to Kim et al. discloses the use of cobalt octoate and xylene group-containing polyamides for use in multi-layer extrusion blow-molding for improved clarity. Extrusion blow-molding minimizes the orientation of the polyamide domain size compared to injection stretch blow molding containers. No color data is given.
There is a need for an improved gas barrier polyester composition that can be injection stretch blow molded as a monolayer container that has reduced yellowness and adequate haze. This is particularly required for containers that require a long shelf life, such as beer and other oxygen sensitive materials. None of these patents disclose how this balance of properties can be achieved.